Rotary machine equipped with a thrust balancing arrangement

ABSTRACT

A housing (1) of a rotary machine comprises a low-pressure side (2) and a high-pressure side (3), working-fluid inlet and outlet channels, and at least one rotor (7), which when the machine is working is urged by a working fluid towards the low-pressure side (2). The rotor includes a thrust balancing arrangement (15, 16) for relieving the load on the thrust bearings (11) of the machine, through the medium of an auxiliary bearing (17) and in dependence on pressure fluid supplied to the thrust balancing arrangement, the pressure of which fluid is contingent on the operating conditions of the machine. A relatively large part of the axial load is taken-up by an auxiliary thrust bearing (17), which is readily replaceable. The auxiliary bearing (17) is mounted on an outermost part of the rotor journal shaft (18), on the high-pressure side (3) of the rotor, between a detachable locking device (27) for the auxiliary bearing (17) and the thrust balancing arrangement. The thrust balancing arrangement is located inwards of the auxiliary thrust bearing and includes two annular piston-cylinder parts (15, 16) which are axially extendible and which are located in a cylindrical recess (14) in the housing (1).

BACKGROUND OF THE INVENTION

The present invention relates to a rotary machine equipped with a thrustbalancing arrangement.

A machine of this kind comprising two helical rotors which arejournalled in thrust bearings at both ends thereof is known from U.S.Pat. No. 3,388,854. In order to obtain uniform distribution of the loadon the thrust bearings and a long useful bearing life, while avoidingthe transition to larger bearings--which normally presents a problem dueto the lack of space for accommodating bearings of larger diameter--theknown machine is provided with a thrust balancing arrangement comprisinga piston-cylinder device which under the influence of pressure fluidcontingent on one working condition of the machine exerts an axialthrust on one rotor through the thrust bearing on the low pressure sideof the machine. This axial thrust is exerted in a direction opposite tothe direction in which the working fluid acts and also in an oppositedirection to the bias of a spring means acting on the thrust bearing.

The length of the useful life of the machine depends upon the conditionof the thrust bearings. The bearings need to be inspected at regularintervals and must be changed when necessary. A bearing change isdifficult to carry out and requires skill and experience on the part ofthe engineer concerned. For example, when effecting a bearing change itis necessary to dismantle the thrust balancing arrangement, togetherwith associated connections and seals, and then to reassemble the thrustbalancing arrangement and test the efficiency of the seals, whichinvolves further work and also the risk of faults occurring as a resultof dismantling the thrust balancing arrangement, etc.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a machine of theaforementioned kind in which the thrust balancing arrangement isconstructed in a manner which will enable the thrust bearing to bechecked and changed without undue difficulty, and which will extend theuseful life of the thrust bearings.

This object is achieved in accordance with the invention with a machinehaving the characteristic features set forth in the following claims.

The fact that the auxiliary thrust bearing is located on the extremityof the shaft journal and is clamped resiliently between the thrustbalancing arrangement and the spring means, enables the thrust bearingto be checked and changed easily, even by unskilled workmen. Therelative ease with which the auxiliary bearing can be replaced can beutilized suitably by placing a relatively heavy load on the auxiliarythrust bearing and by lessening the load on the remaining bearings to acorresponding extent, therewith prolonging the useful life of thebearings. The auxiliary bearing on the other hand, enjoys a shorteruseful life. This is of minor importance, however, since the auxiliarybearing can be readily changed, for instance when carrying out routinemaintenance service.

The auxiliary thrust bearing may also be active when starting andstopping the machine, when the working fluid is under no pressure, oronly a slight pressure, i.e. at low speeds which result inunproportional wear on the bearing. This is a further reason as to whyit should be easy to replace the auxiliary thrust bearing.

According to one preferred embodiment of the invention, the annularpiston-cylinder device of the thrust balancing arrangement has the formof a "plug-in" unit, therewith enabling said device to be readilyremoved and replaced without risk of causing a leakage as a resultthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference toexemplifying embodiments thereof illustrated in the accompanyingschematic drawings, in which:

FIG. 1 is a side view of a machine constructed in accordance with theinvention;

FIG. 2 is a longitudinal, sectional view of the bearing arrangement onthe high-pressure side of the machine; and

FIG. 3 is a part sectional view showing a modification to the auxiliarybearing illustrated in FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates very schematically a screw compressor which comprisesa housing 1 which has a low-pressure side 2 and a high-pressure side 3,and which incorporates a working-fluid inlet channel 4 and aworking-fluid outlet channel 5, the working fluid being a refrigerantfor example. Journalled for rotation in he housing 1 are two helicalrotors 6, 7. As shown in FIG. 2, which is a horizontal, sectional viewtaken through the geometric centre line of the rotor shafts, a journalshaft 8 on the high-pressure end of the right-hand rotor 7, which is amale rotor and is seen from above, is journalled primarily in a radialbearing 10 and two mutually matching thrust ball-bearings 11. Despitethe difficulties involved with the illustrated arrangement of double,so-called matched ball-bearings 11, such an arrangement is necessary dueto the high axial forces to which the bearings are subjected and therequirement of a long useful life of the bearings, and because the spacearound the journal shaft 8 on this end of the rotor is restricted andcannot accommodate the use of larger thrust bearings.

The bearing arrangement is located in a cylindrical recess 14 in thehigh-pressure end 3 of the housing. The recess 14 also accommodates athrust balancing arrangement in the form of an annular piston-cylinderdevice 15, 16, which is mounted for sliding movement in the recess. Alsoarranged for sliding movement in the recess 14, axially outwards of thepiston-cylinder device 15, 16, is the outer ring of an auxiliary bearing17 and a distance sleeve 18 which abuts resiliently against a cup spring19 located on the inside of a cover plate 20, which closes the recess14.

Mutually facing surfaces of the piston 15 and cylinder 16 definetherebetween an annular chamber 21 which communicates with apressure-medium channel 22 extending through the wall of the housing 1and which accommodates a thrust spring which holds the components apart.In order to prevent pressure fluid leaking from the chamber 21, thepiston 15 is provided with a sealing ring 23 which seals against therecess 14, whereas the cylinder 16 is provided with a first sealing ring24, which seals against the recess 14, and a second sealing ring 25,which seals against the piston 15.

The inner rings of the radial bearing 10 and the thrust bearings 11, adistance sleeve 26, and the inner ring of the auxiliary thrust bearing17 are clamped on the journal shaft 8 by means of a lock plate 27 whichis firmly screwed onto the end of said shaft.

The auxiliary bearing 17 is of the kind which is able to transfer thrustin both directions. When the rotary machine is stationary or when thepressure acting on the fluid in the chamber 21 is low, the rotor 7 isheld pressed towards the low-pressure side 2 of the cup spring 19, theforce of which is transmitted to the rotor 7 through the distance sleeve18, the auxiliary bearing 17, the distance sleeve 26, and the innerrings of respective bearings 11.

When the rotor machine is started and begins to build up speed, thepressure exerted by the working medium on the end surfaces of the rotors6, 7 on the high-pressure side will increase, therewith increasing theload on the thrust bearings 11. The pressure acting on the fluid in thechamber 21 will also increase at the same time, causing the piston 15 tobe brought into abutment with the outer rings of respective bearings 11and the cylinder 16 to be brought into abutment with the outer ring ofthe auxiliary bearing 17, against the action of the cup spring 19. Thelock plate 27, and therewith the whole of the rotor 7, will thus beurged towards the high-pressure side 3 of the machine, therewithreducing the load on the bearings 11.

By mutually adapting the pressure in the chamber 21 and the area of thecylinder 16 in said chamber, it is possible to distribute the loadexerted axially by the rotor 7 on the bearings 11 and the auxiliarybearing 17 in a manner which will afford the requisite length of usefullife of the bearings 11. It is possible to accept, without detriment, arelatively heavy load on the auxiliary bearing 17, which also has totake-up the load exerted by the cup spring 19, since the auxiliarybearing can be changed readily as a matter of routine when carrying outa service, without involving either the bearings 11 or thepistoncylinder device 15, 16 and its connection 22. Removal of the coverplate 20 and the lock plate 27 enables the sleeve 18 and the auxiliarybearing 17 to be withdrawn from the recess 14. If necessary it is alsopossible to withdraw the thrust balancing arrangement 15, 16 withoutneeding to touch the pressure-fluid connection.

The auxiliary bearing need not be a bearing of the kind illustrated inFIG. 2, which is capable of taking up axial loads in both directions,but may comprise two separate bearings, for instance as illustrated inFIG. 3. With regard to the balancing of thrust, the FIG. 3 embodimentincludes a bearing 30 which corresponds to the bearing 17 of the FIG. 2embodiment. However, the embodiment illustrated in FIG. 3 includes afurther bearing 31 which is intended to transmit thrust from the cupspring 19 to the lock plate 27 at low machine speeds and when themachine is stationary, this further bearing being located between theaforesaid two components and being centred on the lock plate by means ofa hub 32. This solution is less refined than the solution afforded bythe FIG. 2 embodiment and also has the disadvantage that the bearing 31is constantly subjected to pressure by the cup spring 19, to a greateror lesser extent.

I claim:
 1. A rotary machine, comprising:a housing (1) having alow-pressure side (2), a high-pressure side (3), a working-fluid inletchannel (4) for receiving a working fluid, a working-fluid outletchannel (5), thrust bearing (11) mounted in the housing, a rotor (7)which is rotatably journalled in the housing by means of a rotor journalshaft (8) and which during rotation is subjected to an axial load by theworking fluid in a direction towards the low-pressure side (2) andtowards the thrust bearings (11), and a thrust balancing arrangement(15, 16) in the housing, and said rotor also being subjected to an axialload in a direction towards the high-pressure side (3) by the thrustbalancing arrangement (15, 16); the thrust balancing arrangementcomprising an auxiliary thrust bearing (17), an axially acting springmeans (19) for urging the rotor (7) towards the low-pressure side (2) ofthe housing, and a piston-cylinder device which, under the influence ofpressure fluid contingent on the operating conditions of the machine,partially relieves a load on the thrust bearings (11) by means of theauxiliary thrust bearing (17) which is arranged for limited movementagainst the action of the axially acting spring means (19), the springmeans (19) generating an urging force sufficient to hold the rotor (17)urged towards the low-pressure side (2) when the thrust balancingarrangement (15, 16) is substantially inactive when starting andstopping the machine; a locking device (27) detachably mounted on anoutermost part of the rotor journal shaft (8) at the high-pressure side(3) of the housing; the auxiliary thrust bearing (17) being mounted onan outermost part of the rotor journal shaft (8) at the high-pressureside (3) of the housing, between the locking device (27) which locks theauxiliary thrust bearing (17) and the thrust balancing arrangement (15,16); and the thrust balancing arrangement being located axially inwardsof the auxiliary thrust bearing (17) and the pistoncylinder device ofthe thrust balancing arrangement comprising two annular parts (15, 16)which are axially expandable in a cylindrical recess (14) in the housing(1).
 2. The rotary machine of claim 1, wherein the auxiliary thrustbearing (30 FIG. 3) comprises:a roller bearing having an inner ringwhich is secured on the journal shaft (8) by means of the locking device(27); and an outer ring which is located between the thrust balancingarrangement (15, 16) and the spring means (19) via an outer ring of afurther roller bearing (31) having an inner ring mounted on the journalshaft (8), said further roller bearing (31) transferring an axial forcebetween the spring means (19) and the journal shaft (8).
 3. The rotarymachine of claim 1, wherein the auxiliary thrust bearing comprises:aball-bearing (17) capable of taking-up axial forces in both directions,and having an inner ring which is secured on the journal shaft (8) bymeans of the locking device (27), and an outer ring which is locatedbetween the thrust balancing arrangement (15, 16) and the spring means(19).
 4. The rotary machine of any one of claims 1, 2 or 3, wherein theannular piston-cylinder device of the thrust balancing arrangement (15,16) further comprises:a radial chamber (21) for accommodating pressurefluid; two annular sealing devices (23, 24) which are arranged on thethrust balancing arrangement and which sealingly abut the cylindricalrecess (14) in the housing; the radial chamber (21) being arrangedbetween said annular sealing devices (23, 24); and a pressure fluidchannel (22) provided in the housing (1) and discharging into thecylindrical recess (14) at a location opposite the radial chamber (21).5. The rotary machine of any one of claims 1, 2 or 3, wherein saidspring means (19) comprises a cup spring.